In 1895, a German Physicist, W. C. Röentgen, discovered X-Rays. He pointed, when high speed electrons are bombarded on a clean metal surface radiation of very short wavelength are emitted. X-rays are electromagnetic radiations of very short wave length and very high frequency. Wave length of x-rays varies from 0.001 to 10 nm (10-2 Ao to 102 Ao).
How X-rays are produced?
Production of X-Rays:
There are three methods of producing x-rays.
- Roentgen Method (1895)
- Coolidge Method
- DW Kerst Method (1941), using betatron (an electron accelerating machine)
Roentgen modified discharge tube in shape as shown in figure below. He evacuated air from the tube by vacuum pump and reduced the pressure to 0.001 mmHg.
A very high potential difference (30,000 to 50,000 volts) was applied between anode and cathode. The cathode rays emitted from cathode ionize the gases present in discharge tube. These gas cations then hit cathode due to high electric potential. So electrons are emitted from cathode. These electrons then rush towards anode and hit it with very high speed and momentum; as a result x-rays are emitted from anode. A curved shaped cathode is used so that the electrons emitted from cathode are focused on a small region of anode and x-rays are emitted from this small region of anode.
Properties of X-Rays:
- X-rays travel in straight line.
- They are not deflected by electric or magnetic fields, so they are neutral rays.
- They ionize gases when passed through them. The ionizing power depends on intensity of the x-rays.
- X-rays produce fluorescence in substances like rock salt NaCl (halite), uranium, glass, compound of calcium and barium etc.
- They like other waves, show reflection and refraction.
- They can be diffracted by crystalline substances.
- They have high penetration power through many substances. Extent of their penetration power is different for different substances.
- X-rays can blacken the photographic plate. The extent of this ability depends on the intensity of x-rays, falling on the plate.
Uses of X-Rays:
- Most important use of x-rays is in medical investigation. Because of their differential penetrating power through the skin, flesh and bone, x-rays cast shadow of bones on the photographic plate and are thus used to locate any fractured bone. x-rays also cast shadow of other body parts so heart enlargement could be detected, also any problem in lungs, stomach, kidney etc could be pointed.
- They are used in XRD (x-ray diffraction analysis) to study crystal structure.
- X-rays are used to measure inter ionic distance in crystals.
- X-rays are used to ionize gases.
- Watson and Crick (in 1953) used x-rays diffraction pattern to study double helix of DNA.
- X-rays are used to determine atomic numbers.
Types of X-Rays:
X-Ray spectra consists of various lines called Kα, Kβ, Kγ, Lα, Lβ, Lγ, Mα, Mβ, Mγ etc.
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